This invention relates generally to an air distribution unit. While the invention is applicable to various types of air distribution units, it is particularly useful in conjunction with a unit adapted to be mounted in the ceiling of a room and adapted to admit air into the room from the outlet of an air duct located above the ceiling.
In a more specific sense, the invention relates to an air diffuser in which a reciprocating pneumatic actuator moves a valve element or damper between open and closed positions relative to the outlet of the air duct. The flow of pressure fluid to the actuator preferably is controlled so as to enable the actuator to move the damper to various positions between its fully open position and its fully closed position and thus effect regulation of the volume of conditioned air delivered to the room. A typical pneumatic actuator includes slidably telescoped piston and cylinder members with one of the members being advanced by pressure fluid to open the damper and being retracted by a spring to close the damper.
In the case of fire, it is desirable to close the outlet of the duct in order to cut off the flow of air from the duct, to prevent smoke from entering the room by way of the duct and to retard heat flow from the room to the structural members above the ceiling. Automatically closable fire dampers for air ducts have existed previously. To the best of my knowledge, however, those dampers are normally held in a fully open position and are closed only in the event of fire. Such a damper is not, therefore, capable of regulating the flow of air into the room under normal conditions.